Many of the overturned convictions were a result of false confessions coming to light or the discovery that no crime was actually committed.

“In a steady number of cases we make horrible mistakes,” report author Samuel Gross, a law professor at the University of Michigan, told U.S. News & World Report.

Seventeen percent of those exonerated in 2013 had at first pleaded guilty to a crime they did not commit. This usually occurred because the defendant was offered a plea bargain, in which a lesser sentence was promised in exchange for a guilty plea.

Gross found that no crime occurred in 27 of the cases. Examples of these mistakes included:

· Joseph Awe of Wisconsin, who served nearly three years in prison for arson until officials realized the fire was an accident.

· Nicole Harris of Illinois who was convicted of murdering her four-year-old son, who it turned out accidentally suffocated while playing with his brother. It was determined that Harris had been coerced into pleading guilty by Chicago police, who—during 27 hours of questioning—pushed and threatened her, forbid her to use the restroom, and prevented her from having food or water. She spent eight years in prison.

Other findings from the report showed the number of exonerations resulting from DNA evidence was down again, which has been the case since 2009.

“I think some DNA exonerations will keep happening, but not in the numbers we saw 10 or 15 years ago,” Gross said. “If the other trends continue, they’ll become a smaller fraction of all exonerations as time goes on.”

Gross partially credits law enforcement organizations for the report’s findings, as 38% of the exonerations were initiated by such groups.